1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having fine patterns and a semiconductor device manufactured by the method. More particularly, the present invention relates to a method of forming a resist pattern used for micro-processing of an LSI semiconductor element, a liquid crystal display panel, or the like. Further specifically, the present invention relates to a method of forming a highly-accurate fine resist pattern.
2. Background Art
FIG. 14 shows resist patterns which are formed on an underlying layer 21 according to a conventional method by exposing the layer to light through a mask held at an optimum focal point by a stepper. In FIG. 14, reference numeral 22 designates a resist pattern having a line width broader than the wavelength of exposing light from the light source of the stepper, and 23 designates a fine resist pattern having a line width narrower than the wavelength of exposing light from the light source of the stepper. As mentioned above, in a case where the underlying layer is exposed to light through the mask held at an optimum focal point, even the existing method enables a resist pattern to be formed substantially faithfully.
FIG. 15 shows resist patterns which are formed on the underlying layer 21 according to the existing method by exposing the layer to light through a mask held out of focus. In FIG. 15, reference numeral 22' designates a resist pattern having a line width broader than the wavelength of exposing light from the light source of the stepper, and reference numeral 23' designates a fine resist pattern having a line width narrower than the wavelength of exposing light from the light source of the stepper. In a case where the underlying layer is exposed to light through the mask held out of focus, no problems are encountered in the formation of the resist pattern 22' having a line width broader than the wavelength of exposing light from the light source of the stepper. In contrast, in a case where the fine resist pattern 23' having a line width narrower than the wavelength of exposing light from the light source is formed, there arises a problem that the line width of a resultant pattern becomes narrower.
FIG. 16 is a plot showing the relationship between the dimension of the resist pattern and defocus for the purpose of explaining the foregoing problem. As designated by line 22a shown in FIG. 16, in a case where a resist pattern of great size is formed, no dimensional variations arise even if the mask of the stepper is slightly defocused. In contrast, as designated by curved line 23a shown in FIG. 16, in a case where a fine resist pattern smaller than the wavelength of exposing light from the light source of the stepper is formed, and if the mask of the stepper is defocused, significant dimensional variations arise, resulting in a resist pattern of undesirable size.
As mentioned above, at the time of formation of a fine resist pattern, the existing photolithography technique has the disadvantage of being incapable of stably forming a resist pattern.
Accordingly, the object of the present invention is to stably form a fine resist pattern smaller than the limit of the wavelength of exposing light by processing photoresist through a chemical mechanism such as diffusion of an acid or decomposition of photoresist.
Another object of the present invention is to provide a method of manufacturing a semiconductor device which uses the thus-formed fine resist pattern, as well as a semiconductor device having the fine pattern manufactured by the method.